Structure, Dynamics, and Rheology of Vitrimers
Structure, Dynamics, and Rheology of Vitrimers
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DOI：
10.1021/acs.macromol.3c01366
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发表时间：
2023-09
期刊：
影响因子：
5.5
通讯作者：
Jianshe Xia;J. Kalow;M. Olvera de la Cruz
中科院分区：
文献类型：
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作者：
Jianshe Xia;J. Kalow;M. Olvera de la Cruz
三聚体是缔合共价自适应网络，其经历可逆的键交换反应，同时随着温度的变化保持固定的交联密度。迄今为止，依赖于宏观流变学的实验研究还不能揭示这些材料的拓扑变化和微观动力学。在这里，粗粒度的分子动力学模拟结合蒙特卡罗方法实施调查的拓扑结构的变化，微观动力学和线性流变学的未纠缠的侧链连接的玻璃体结合粘性劳斯模型（SRM）。我们发现，有一个微小的变化，在拓扑结构与温度。当接近拓扑冻结转变温度Tv时，键交换行为和系统动力学的动力学不均匀性显著增加。应力松弛，弹性模量和损耗模量，以及相对均方位移，特别是在中间和长时间或低频制度，其中的时间-温度叠加原理是满意的模拟结果和SRM的预测之间的定量协议。我们得到了一个缩放崩溃曲线的动态键弛豫时间，零剪切粘度，和水平位移因子，而不引入任何参数，这表明微观和宏观动力学表现出类似的松弛行为，即使在存在环路缺陷。此外，这些结果与SRM预测的结果吻合良好，表明具有快速键交换速率的未缠结玻璃体的线性流变学可以通过基于SRM的单链方法进行分析。
Vitrimers are associative covalent adaptable networks that undergo reversible bond-exchange reactions while maintaining a fixed cross-linking density with changing temperature. To date, experimental studies that rely on macroscopic rheology have not been able to reveal topological changes and microscopic dynamics in these materials. Here, coarse-grained molecular dynamics simulations combined with a Monte Carlo method are implemented to investigate the topological structural changes, microscopic dynamics, and linear rheology of unentangled side-chain-linked vitrimers in conjunction with the sticky Rouse model (SRM). We find that there is a minor variation in the topological structure with temperature. The dynamic heterogeneities of the bond-exchange behavior and the system dynamics increase remarkably when approaching the topological freezing transition temperatureTv. Quantitative agreement between the simulation results and the SRM predictions is observed for the stress relaxation, elastic and loss moduli, and the relative mean-squared displacement, especially at the intermediate- and long-time or low-frequency regimes, where the time–temperature superposition principle is satisfied. We obtain a scaling collapse curve for the dynamic bond relaxation time, the zero-shear viscosity, and the horizontal shift factors without introducing any parameters, suggesting that the microscopic and macroscopic dynamics exhibit a similar relaxation behavior even in the presence of loop defects. Moreover, these results are in good agreement with those predicted by the SRM, indicating that the linear rheology of unentangled vitrimers with a fast bond-exchange rate can be analyzed via a single-chain approach based on the SRM.